This invention relates generally to a pig for a fluid conducting system and more particularly, but not by way of limitation, to a pig for separating a first fluid from a second fluid in a reactor tube of a continuous reactor system wherein a polymer is reacted and ejected for flooding a hydrocarbon-bearing formation through which a well is drilled.
In a fluid conducting system, articles referred to as "pigs" are used to separate fluids moving through the system. For example, in a continuous polymer reactor system disclosed in U.S. patent application Ser. No. 615,440 now U.S. Pat. No. 4,595,566, pigs are used to separate different volumes of polymers that are moved through the tubing in the reactor system in route to being injected into a well during a tertiary hydrocarbon recovery operation. In this exemplary system, movement of the pig is bidirectional.
The general purpose of a pig used in a fluid conducting system is to provide a movable fluid-sealing barrier between the fluids. The sealing nature of such pig prevents unwanted intermingling of the separate volumes of fluid. The sealing function is also important in the exemplary reactor system because if leakage occurs across the pig, the synchronization of the flows within the reactor system can be lost.
Another function of such a pig is to provide some means of actuating a signal signifying the location of the pig. This is particularly useful in a system such as the exemplary reactor system wherein it must be determined when the pig reaches an end of a reactor tube so that valve states can be changed to reverse the direction of fluid flow, whereby the fluid volumes and the pig are moved in the opposite direction.
One type of pig which has been tried in the polymer reactor system is an article referred to as a prover ball, a substantially spherical member made of a relatively hard substance, heretofore known to be used in proving meters of fluid flow systems. When used in the reactor system described in U.S. patent application Ser. No. 615,440, the prover ball would sometimes hang up in the flanged joints and allow fluid leakage between different volumes of the polymer, thereby allowing intermingling of the polymer and losing synchronization among the timerelated volumes of moving polymers. To indicate its arrival at a predetermined location, the ball would mechanically engage and deflect a mechanical switch, which switch would ultimately become inoperative due to the highly viscous polymer leaking into the switch housing.
From the foregoing example, there is the specific need for an improved pig which more satisfactorily works in a continuous polymer reactor system to maintain proper sealing and synchronization between separate volumes of fluid. Such a pig must be bidirectionally operable for this specific use. Such a pig should also include a type of location signal actuating means which is not affected by the fluid with which the pig is used (such as the highly viscous polymer of the exemplary reactor system). Such a pig should also be, in general, adaptable for use in any suitable fluid conducting system.